The present invention relates to measuring and recording devices and techniques for compensating electronic measurement systems for the effects of electronic component drift over time and temperature. By way of example but without limitation, one embodiment of the present invention relates to temperature measuring and recording devices and techniques which perform high resolution temperature difference measurements, on the order of micro-degrees centigrade.
The method and apparatus of the present invention accurately resolve extremely small differences in electrical signals, in a very low cost, highly portable apparatus that can be battery operated. In an exemplary embodiment, the method and apparatus of the present invention are directed to the measurement of temperature differences, on the order of micro-degrees centigrade, by utilizing predictable behavior in the relative time drift of thermal offset curves, for various circuit elements, including a difference signal means optionally having amplification for providing an amplified difference signal, an ambient temperature amplification means, and an analog to digital converter means. In an initial calibration mode, preferably performed at the time of manufacture, the exemplary embodiment records several thermal offset curves, stored in memory, which correlate ambient temperature measurements to offset measurements acquired from the ambient temperature amplification means and the difference signal means, with both of said means connected to a measurement bridge, comprising two thermistors and two resistors, for measuring ambient temperature and temperature differences (via nodes of the measurement bridge). Thermal offset curves recorded in the initial calibration mode, correlating ambient temperature measurements to measurements from the difference signal means, include one curve recorded with both inputs of the difference signal means held at equal potential and another curve recorded with both thermistors of the measurement bridge held at the same temperature, over a given ambient temperature range. Another thermal offset curve, preferably recorded at the time of manufacture, correlates measured ambient temperature from the ambient temperature amplification means to measurements from the ambient temperature amplification means, with inputs to said ambient temperature amplification means shorted together or, alternatively, shorted together and connected to one or more reference signals (such as system ground), which in the exemplary embodiment are preferably voltages from a reference resistance bridge, preferably comprising substantially time stable (not necessarily temperature stable) resistors. The method and apparatus of the present invention require few components, and no precision active or passive components, resulting in low power consumption, and low cost. The method and apparatus of the present invention overcome time and temperature component drift, by utilizing the fact that the thermal offset curves, acquired in the initial calibration mode (preferably at the time of manufacture), drift with time in a predominantly linear fashion relative to one another. Consequently, during normal operation, these offset curves representing temperature drift behavior, among electrical components, can be updated for time drift, at a single, current arbitrary ambient temperature, the measurements for which can be obtained quickly and applied as a time drift correction to thermal offset curves, without interrupting normal system operation. Additionally, the present invention dynamically tracks cumulative system errors associated with the method of the present invention, in order to dynamically calculate optimal system resolution, based upon current operating conditions (rather than based upon more general component drift specifications).
Various electronic systems exist for measuring extremely small differences in sensor measurements, such as temperature, for use in biological and physical analyses. It is known in the art that active and passive electronic components in such systems are subject to time and temperature drift, and that under normal operating conditions, the amplitude of time and temperature component drift is typically much greater than the amplitude of other inaccuracies generated by system components, such as amplifier noise voltage, noise current, and resistor noise. Consequently, component time and temperature drift are significant limiting factors to high resolution measurements, such as temperature difference measurements. To address the problem of component drift in electronic measurement systems generally, various approaches to compensate for drift have been devised.
For example, U.S. Pat. Nos. 5,253,532 (Kamens); 5,042,307 (Kato); 4,611,163 (Madeley); and 3,831,042 (La Claire) disclose electronic measurement systems (principally directed to pressure sensing, in the preferred embodiments) which include additional hardware components that change their electrical resistance, or other electrical parameters, with ambient temperature, in such a way as to compensate for thermal drift in measurement systems to which they are electrically connected. While such hardware compensation systems provide some compensation for thermal drift inaccuracies, they do not compensate for component drift over time, particularly the drift of sensors, such as thermistors. This would be sufficient to preclude temperature difference measurements, with resolution on the order of micro-degrees centigrade, if these techniques were applied to that purpose. Additionally, such hardware based compensation techniques do not readily compensate for component drift, resulting from the combined time drift characteristics of multiple system components, located at different parts of the system, with different thermal drift characteristics, and subject to non-uniform aging. In any case, the ability of the above hardware based compensation systems and techniques to compensate for system thermal drift are limited by the extent to which the particular technique tracks with thermal drift of the overall system, over time and temperature. Consequently, such techniques would not provide sufficient compensation for component time and temperature drift to permit differential temperature measurements, with resolution on the order of micro-degrees centigrade, if these techniques were applied to that purpose.
Other hardware compensation techniques, such as disclosed in U.S. Pat. Nos. 5,616,846 (Kwasnik); 5,171,091 (Kruger et al.); and 5,132,609 (Nguyen), require a time and temperature stable reference signal, and U.S. Pat. No. 5,351,010 (Leopold et al.) requires the use of precision analog amplification hardware and costly time and temperature stable resistors. The required precision analog components in these systems results in increased cost, complexity, and power consumption. Moreover, these systems do not compensate for time drift of passive components, such as thermistors, which would be sufficient to preclude temperature difference measurements, with resolution on the order of micro-degrees centigrade, if these systems were applied to that purpose.
Additionally, U.S. Pat. Nos. 5,162,725 (Hodson et al.); 5,065,613 (Lehnert); 4,958,936 (Sakamoto et al.); and 4,464,725 (Briefer) describe electronic measurement systems which compensate for thermal drift, and other system inaccuracies, by utilizing a computer, and memory for storing known temperature behavior of a measurement system, at various calibration temperatures. That is, system inaccuracies due to temperature drift are recorded at specific calibration temperatures. This stored temperature behavior is then used to interpolate system inaccuracies due to thermal component drift at operational temperatures within the calibration range. This has been accomplished by using mathematical formulae to model thermal offset curves (e.g., using a parabolic interpolation, such as the LaGrange method, to plot offset curves, based upon discrete offset measurements, at discrete ambient temperatures), and then during normal operation, using a said formula, with a current ambient temperature measurement, to determine expected circuit offsets for the current ambient temperature, so that actual system measurements during normal operation can be adjusted for the effects of said expected circuit offsets. The prior art measurement systems, which utilize a computer, can provide time and temperature compensation based only upon the most recent reference calibration data, the acquisition of which requires that the system be cycled through an entire temperature range, and is sufficiently time consuming to prevent, or significantly interrupt, normal system operation. Other techniques that utilize software compensation, such as disclosed in U.S. Pat. No. 4,532,601 (Lenderking et al.), as well as in U.S. Pat. No. 4,464,725 (Briefer, referred to above), require the use of a time and temperature stable reference signal, which increases cost, complexity, and power consumption. U.S. Pat. No. 4,959,804 (Willing) utilizes time and temperature stable passive components, which, even with costly bulk metal foil, or wirewound, resistors, would not provide the accuracy necessary in temperature difference measurements, with resolution on the order of micro-degrees centigrade, if this technique were applied to that purpose. Such time and temperature stable bulk metal foil resistors (e.g., manufactured by Vishay Electronics Foil Resistors, of Malvern, Pa.) and wirewound resistors, such as manufactured by Dale Electronics, of Norfolk, Nebr., are one to two orders of magnitude more expensive than standard metal film resistors, which provide comparable time stability, but are not nearly as temperature stable. Furthermore, U.S. Pat. No. 4,959,804 (Willing, referred to above) updates a previously recorded temperature curve according to the two endpoints of the curve, thereby ignoring variations that might occur at intervening points along the curve, over time, as well as time drift in temperature measuring thermistors, which drift sufficiently over time to invalidate temperature difference measurements, with resolution on the order of micro-degrees centigrade, if it were applied to the purpose of high resolution differential temperature measurements. U.S. Pat. No. 4,651,292 (Jeenicke) relies on updating a point on a measurement curve, requiring, however, the restriction that the sensor curve characteristic be linear (not the case with temperature sensors, such as thermistors, and not sufficiently so, to provide resolution on the order of micro-degrees centigrade, even with known thermistor linearization techniques) and that ambient temperature measurements not drift with time, to the extent that measurement accuracy would be affected, making this technique unsuitable for a differential thermometer with resolution on the order of micro-degrees centigrade, if such a technique were to be applied to that purpose.
In the above approaches, as they would relate to a temperature difference measurement system, utilizing a pair of thermistors (e.g., in a thermistor-resistor bridge arrangement), it is relevant to note that differences in thermistor resistance-temperature curve characteristics, between two thermistors, result in a difference in the two thermistor resistances, throughout an ambient temperature range, that varies significantly with ambient temperature. For instance, YSI 460 series xe2x80x9cSuper-Stable Thermistorsxe2x80x9d, manufactured by YSI, Incorporated, of Yellow Springs, Ohio, are characteristic of well matched, commercially available thermistors, and are matched to within 0.05 Cxc2x0 of each other, between 0 Cxc2x0 and 50 Cxc2x0. This means that within the 0 Cxc2x0 to 50 Cxc2x0 range of operating temperatures, the difference in thermistor resistances may change by as much as 0.001 Cxc2x0, relative to each other, for each ambient temperature change of 1 Cxc2x0, a significant amount in measurements intended to resolve temperature differences on the order of micro-degrees centigrade. The above approaches, as they would relate to a temperature difference measurement system, utilizing a pair of thermistors, do not provide a means to compensate for this effect. Additionally, in order to minimize common mode amplifier error, the use of bipolar power to the measurement bridge is often preferred in the above prior art, as are high precision amplifiers, which typically require bipolar power, resulting in added cost and complexity, compared to a single-ended power supply architecture.
In U.S. Pat. No. 5,295,746 (Friauf et al.), directed specifically to the technical field of temperature difference measurement, with resolution on the order of micro-degrees centigrade, it is pointed out that a number of digital thermometers exist, which, however, have accuracy limitations on the order of one hundred milli-degrees centigrade. U.S. Pat. No. 5,295,746 addresses some of the limitations of the prior art, in this respect, by using a computer to maintain a thermistor-resistor bridge in a balanced state, to provide a means for adjusting thermistor power dissipation and to null out thermally generated offsets in the system""s analog to digital converter, digital to analog converters, and amplifiers, for a given thermistor power dissipation, for the current ambient temperature. However, this requires that the bridge circuit be balanced with extreme accuracy, requiring the addition of two digital to analog converters to the circuit, preferably employing high resolution, in order to achieve high resolution temperature difference measurements, resulting in added component count, cost, and power consumption. Additionally, no means is provided to compensate for time drift of thermistors, which typically amounts to ten or more milli-degrees/year (e.g., YSI 44018, manufactured by YSI Incorporated, of Yellow Springs, Ohio), a significant figure in temperature difference measurements, intended to approach micro-degree centigrade resolution. Additionally, software calibration of this system, for a current ambient temperature, is undertaken at the time when temperature difference measurements are undertaken, yet requires that bridge thermistors be completely powered down first, so that there is zero voltage potential across the bridge during calibration. That is, system calibration followed by continued operation in the temperature difference measurement mode must be undertaken by first powering down the bridge thermistors, and then powering them up again. Due to self-heating properties of thermistors, when a voltage is placed across thermistors, time is required for the thermistors to reach equilibrium with ambient temperature, which they do asymptotically. In cases where temperature difference measurements on the order of micro-degrees centigrade are to be resolved, this powering down and then powering up of the bridge, until the thermistors are within micro-degrees centigrade of equilibrium, adds significant time to the calibration process. Since each calibration offset measurement is associated with a specific ambient temperature, a calibration measurement (and, therefore, an ambient temperature) must be associated with each temperature difference measurement. Calibration measurements performed before and after a measurement run can conceivably be used to interpolate linear changes in ambient temperature with time, during a measurement run, but this places an unrealistic limitation on a measurement system which desirably operates under normal atmospheric conditions, in which ambient temperature changes may not be linear with time. Therefore, a calibration measurement must be undertaken for each temperature difference measurement, in which ambient temperature may not have undergone a linear change, thus adding significant time to the measurement process. Similarly, U.S. Pat. No. 5,351,010 (Leopold et al., also mentioned above) requires that current be reversed through zero, in resistive sensors, for each calibration, as well as requiring precision circuitry, that increases cost, complexity, and power consumption.
Additionally, the prior art does not provide a means to dynamically quantify compensation inaccuracies, resulting from the particular drift compensation technique used. These inaccuracies, inherent in the above compensation techniques, may vary widely, depending on specific operating conditions, such as: ambient temperature; number and location of temperature compensation/sensing devices in the system; thermal and time drift homogeneity among system components; time elapsed since a reference calibration (where relevant); and system warm-up status. In the above prior art, a general specification based upon a combination of individual system component drift tolerances, taken as a whole, can conceivably be computed to account for temperature and time drift limitations of a system. Based upon a given calibration, and/or compensation technique, over an intended temperature span, such a computation could be used to provide a limitation to achievable resolution in the above prior art, in a given operating environment, for a given calibration/compensation technique, over an expected temperature range of operation. However, in order to be reliable, such a computation would need to take into consideration factors which include long term time-drift characteristics of active and passive components, including amplifiers, and mixed-mode devices, such as analog/digital converters, as well as time drift of passive components, such as resistors and thermistors. An additional source of error to take into consideration, in devices expected to perform to specification when they are turned on, includes time versus drift behavior during system warm-up. Consequently, although a general specification for the ability of a technique to compensate for component time and temperature drift may be calculated, by combining manufacturer supplied drift specifications for relevant components, the actual value of errors associated with uncompensated component drift, in a given compensation technique, may change significantly, depending on the above factors, so that rather than being optimized, based upon current operating conditions, such a calculated specification must be set high enough to anticipate worst case conditions.
Such calculated resolution limits, for a given system, over a given temperature span, are often used to estimate performance in bridge measurement systems. However, it would be highly advantageous in detecting extremely small variations, approaching the limitations of modem electronics, to dynamically use limitation information that improves upon such absolute estimates, whenever possible. For example, system limitation specifications can be significantly enhanced by using such information as: elapsed time since a last reference calibration; empirically determined tolerance of temperature versus offset drift curves, over time; and elapsed time since power-up. In the above prior art, no means is provided to dynamically and efficiently account for collective circuit limitations, associated with a drift compensation method, in such a way as to provide an accurate, instantaneous indication, or continuous system control, reflecting optimum achievable system accuracy, under the drift compensation method, and based upon current operating conditions.
In spite of advances in bridge measurement systems, and in particular, high resolution temperature difference measurement systems, there remains a need for a high resolution measurement system, such as a differential thermometer, utilizing a minimum of low cost components, consuming minimal power (permitting battery powered operation), and operable from a single-ended power supply, that provides accurate temperature compensation, and that can be calibrated during normal operation, for temperature drift, and time drift of system components, without significantly interrupting operation in the field, and that sufficiently compensates for time drift of passive components, such as thermistors, so that a specified system resolution, in the case of the differential thermometer on the order of micro-degrees centigrade, is achievable. Additionally, there remains a need for such a system which provides an instantaneous indication of system resolution limitations, based upon current operating conditions, which can be reported to the user, or employed to continuously and automatically effect system reporting in such a way as to dynamically provide optimal resolution, rather than using a single specification based upon a combined estimate of expected system tolerances.
It is therefore a general object of the present invention to provide a very low cost means of accurately measuring small signals and signal differences.
It is a more particular object of the present invention to provide a very low cost system for accurately measuring small temperature differences, on the order of micro-degrees centigrade, that can provide accurate compensation for time and temperature component drift, without significantly interrupting normal system operation.
It is another object of the present invention to provide a very low cost means of measuring small temperature differences, on the order of micro-degrees centigrade, such that the system can be operated under normal atmospheric conditions, and calibrated during normal operation, for time and temperature drift of active system components, such as amplifiers and analog to digital converters, and such that said calibrations can be readily, and quickly, performed in the field, to permit accurate operation, with resolution on the order of micro-degrees centigrade, without significantly interrupting normal operation.
It is yet another object of the present invention to provide a very low cost means of measuring small temperature differences, which sufficiently compensates for time drift of passive components, such as thermistors and feedback resistors, to permit temperature difference measurements, with resolution on the order of micro-degrees centigrade, and such that said sufficient compensation can be performed readily, and quickly, in the field, without significantly interrupting normal operation.
It is still another object of the present invention to provide a very low cost, high resolution difference measurement system, with continuous indications of measurement system resolution capability, based upon current operating conditions, such that said resolution capability can be continuously reported to the user or employed to automatically and continuously effect system reporting in such a way as to dynamically provide optimum system resolution.
Another object of the present invention is to provide a very low cost system for measuring other parameters, such as electrical signals, pressure, flow, or other variables, that can provide accurate compensation for time and temperature component drift, resulting in highly accurate measurements without significantly interrupting normal system operation.
Still other objects and advantages of the present invention will be apparent from the specification which follows.
The various embodiments of the present invention improve over prior art systems and techniques for measuring low level signals, such as signals representative of differential temperature, by reducing the number and cost of components required to achieve high resolution measurements, such as difference signal measurements. One embodiment of the present invention improves over prior art high resolution difference measurement systems, by permitting accurate compensation for time and temperature drift of both active and passive system components, at a single current arbitrary temperature within a range of ambient temperatures, to permit temperature difference measurements, with resolution on the order of micro-degrees centigrade, and such that critical calibrations can be performed without interrupting normal system operation. Additionally, the various embodiments of the present invention improve over prior art high resolution measurement systems, by providing a continuous indication of measurement system resolution capability, based upon current operating conditions, and which can be continuously reported to the user, or employed to automatically and continuously effect system reporting in such a way as to dynamically provide optimum system resolution, as opposed to limiting optimum resolution to a general specification, based upon individual component performance over a temperature range.
Generally, in accordance with the present invention, an improved signal measurement method and apparatus are provided, which accurately resolves extremely small differences in electrical signals, in a very low cost, highly portable apparatus that can be battery operated, by utilizing predictable behavior in the relative time drift of offset curves, such as thermal offset curves, for various circuit elements of the apparatus, including difference signal means and ambient condition measurement means, such as ambient temperature amplification means. In an exemplary embodiment, which measures temperature differences, with resolution on the order of micro-degrees centigrade, the difference signal means includes a difference amplifier, which amplifies a voltage difference between two nodes of a measurement bridge, comprising two thermistors and two resistors, such that said voltage difference represents a temperature difference between said thermistors. Additionally, in the exemplary embodiment, the ambient temperature amplification means amplifies the difference in voltage between one of said nodes of said measurement bridge (the voltage of which varies with ambient temperature) and a reference node, the voltage of which is provided by a reference bridge (preferably comprising resistors, with substantially time stable temperature-resistance curves), in order to provide a signal representative of ambient temperature. It will be appreciated by those skilled in the art that the said voltage of the reference node may alternatively be provided by system ground or a reference voltage device of the type well known in the art, thereby eliminating the need for the said reference bridge, and that parameters other than temperature can be measured.
In an initial calibration mode (called reference calibration mode, in accordance with the present invention), preferably performed at the time of manufacture, thermal offset curves are recorded, which correlate ambient temperature measurements to offset measurements from both the ambient temperature amplification means and the difference signal means (said measurements are converted to digital form by the analog to digital converter means). The thermal offset curves include: one curve, recording measurements from the difference signal means, with both thermistors of the measurement bridge held at the same temperature, over the ambient temperature range; another curve, recorded with both inputs of the difference signal means held at equal potential, over the ambient temperature range; and yet another curve, correlating ambient temperature, over the ambient temperature range, to measurements from the ambient temperature amplification means, with both inputs of said ambient temperature amplification means connected to voltages of a reference resistor bridge, preferably comprising resistors having a substantially time stable temperature-resistance characteristic.
One of said thermal offset curves, recorded during operation in the reference calibration mode (said curve referred to as a difference temperature curve or, more generally, as a physical variable difference curve, in accordance with the present invention), correlates difference signal measurements to ambient temperature measurements, with the two thermistors of said measurement bridge held at the same temperature, throughout operation in the reference calibration mode. Consequently, the resulting difference temperature curve can be used, during normal operation, to correlate any ambient temperature measurement, within the range of calibrated ambient temperatures, to a point on the difference temperature curve, corresponding to the expected temperature difference, if both thermistors were at the same said measured ambient temperature. That is, during normal operation, a measured ambient temperature can be correlated to an expected temperature difference measurement (corresponding to zero temperature difference) to provide an offset, which can be used to adjust any measured difference temperature, by said offset, in order to compensate for non-matching temperature-resistance characteristics, between thermistors, over the ambient temperature range in which operation in the reference calibration mode was performed. Note that this does not compensate for drift of active components associated with the difference measurements, such as amplifiers and analog to digital converters, which are preferably compensated for as indicated below.
Another thermal offset curve, recorded during operation in the reference calibration mode, is referred to as a difference reference curve, in accordance with the present invention, and correlates ambient temperature measurements to an amplified difference between the two inputs of the difference signal means of the preferred embodiment, when both said inputs are shorted to the same potential, over the ambient temperature range in which the reference calibration mode is performed. The difference reference curve is used to compensate for time drift of the difference temperature curve, over the ambient temperature range in which the reference calibration mode was performed, and thus is used to compensate for time and temperature drift of active components associated with difference signal measurements, in contrast to drift of passive measurement bridge components, such as thermistors, which typically drift at different rates over time relative to active components, such as amplifiers and analog to digital converters. Note that the difference reference curve is acquired with both inputs of the difference signal means shorted to the same potential, in contrast to the difference temperature curve, which is acquired with both thermistors held at the same temperature, over the ambient temperature range, in which the reference calibration mode is performed.
Finally, another thermal offset curve, recorded during operation in the reference calibration mode, is referred to as an ambient reference curve, in accordance with the present invention, and correlates ambient temperature measurements to an amplified difference between two nodes of said reference bridge, as amplified by the ambient temperature amplification means. The ambient reference curve is used to compensate for time and temperature drift of ambient temperature measurements, by translating the positions of other thermal offset curves, acquired during the reference calibration mode, relative to ambient temperature measurements. Both the ambient reference curve and the ambient temperature scale, against which all thermal offset curves are measured, are shifted by the method of the present invention, utilizing at least one measured point and recorded points on the ambient reference curve, along with related measured and recorded ambient temperatures, such that a compensation is achieved for both the ambient temperature amplification means and passive measurement bridge components, associated with ambient temperature measurements.
The method of the present invention does not require that amplifiers of either the ambient temperature amplification means, nor difference signal means, provide precision performance (such as low offset voltage, low temperature drift, low common mode rejection, or, in the case of battery powered embodiments, in which battery voltage may vary over time, low power supply rejection). Nor does the method of the present invention require that the reference or measurement bridge employ time and temperature stable resistors. However, bridge and feedback resistors of the preferred embodiment of the present invention are preferably time stable, such as those of standard metal film composition (e.g., manufactured by Dale Electronics, of Norfolk, Nebr.), which offer stability over time, comparable to much more costly temperature stable, and time stable, bulk metal foil resistors (manufactured by Vishay Electronics Foil Resistors, of Malvern, Pa.), or wirewound resistors (such as manufactured by Dale Electronics, of Norfolk, Nebr.).
The method of the present invention overcomes time and temperature component drift, by utilizing the fact that the thermal offset curves, over a given ambient temperature range, drift with time in a predominantly linear fashion, relative to one another, in response to component time drift (e.g., resulting from active component offset voltage drift, common mode variations, power supply variations in battery powered embodiments, and temperature-resistance curve drift, over time, of thermistors and resistors associated with amplifiers and resistance bridges). Hence, the thermal offset curves, representing temperature drift behavior, which vary among each other in a predominantly linear fashion over time, within a calculable accuracy, are acquired, and stored in memory, so that during normal operation, these curves can be updated for time drift, at a single, current arbitrary ambient temperature, the measurements for which are obtained quickly (in a standard calibration mode, in accordance with the present invention) and applied as a time drift correction to thermal offset curves, without interrupting normal system operation. This method of the present invention enables compensation for time and temperature drift of active components and passive components sufficiently to permit accurate resolution of temperature differences, for example, on the order of micro-degrees centigrade.
Non-linear time drift, primarily associated with passive component drift over time (e.g., time drift of thermistors and feedback resistors, resulting in gain drift) is substantially compensated by the method of the present invention, over many months of operation, without requiring a re-acquisition of thermal offset curves over a temperature range, because such gain drift over time is manifested to a much smaller extent as a change in curve xe2x80x9cshapexe2x80x9d, rather than as a linear curve translation. However, such non-linear changes in thermal offset curve shape, over time, will eventually affect the accuracy of measurements. The extent to which the effects of non-linear drift over a given time are compensated corresponds to a maximum time period, within which re-acquisition of thermal offset curves is required, in order to achieve a given measurement accuracy. This maximum period depends substantially on the time stability (not the temperature stability) of passive components, especially gain feedback resistors. In order to determine the maximum period between re-acquisition of offset curves that is required in order to achieve a given accuracy, operation in the reference calibration mode is preferably performed on two occasions, at the time of manufacture, utilizing a constant temperature bath, capable of providing at least two known, repeatable temperatures. Nevertheless, the method of the present invention permits a re-acquisition of thermal offset curves over an arbitrary temperature range, so that subsequent re-acquisitions of thermal offset curves can be performed, at any time, by the end user, without such costly calibration equipment.
Additionally, the method of the present invention dynamically tracks cumulative system errors, associated with drift compensation, and based upon current operating conditions, in order to dynamically calculate optimal system accuracy, based upon current operating conditions (rather than based upon a combination of more general component drift specifications). Once quantified, the calculated optimal system accuracy, based upon current operating conditions, can be used to dynamically control system reporting, to reflect achievable accuracy.